1. Field of the Invention
The present invention relates to a substrate core and method for fabricating the same. More particularly, the present invention relates to a substrate core having high thermal conductivity and high electrical conductivity and a method of fabricating the same.
2. Description of the Related Art
The information technology products in this business world have becoming increasingly important. As new models continue to be introduced, current electronic products not only offer diversifying functions but have developed to be more miniaturized, with the operating performance upgraded to be more stable. As the electronic products become miniaturized, heat dissipation has become a major issue in high power chips, such as microprocessors or light-emitting diodes, because a stable operation depends on the rapid heat dissipation from the heat generating sources. For a chip packaging structure having a chip on a substrate, the substrate is one of the principal channels for dissipating heat from the chip. Therefore, the thermal properties of the substrate will directly affect the reliability of the chip operation.
FIG. 1 is a schematic cross-sectional view of a conventional substrate. To fabricate the substrate shown in FIG. 1, a core layer 110 is provided and then a plurality of holes 112 passing through the core layer 110 are formed. Thereafter, a reverse oxidation reaction and an electroplating process are performed to form metallic layers 122, 124, 126 on the top/bottom surface of the core layer 110 as well as the inner wall of the hole 112. After that, photolithography and etching processes are performed to pattern the metallic layers 122 and 124. Then, insulation layers 132, 134, 136, 138 and patterned metallic layers 142, 144 are separately formed on each side of the core layer 110. Through the metallic layers 122, 124 and 126, the patterned metallic layers 142 and 144 on each side of the core layer 110 can be electrically connected.
In the aforementioned substrate 100, the metallic layer 126 with good thermal conductivity is formed only on the inner wall of the hole 112 in the core layer 110 without filling the entire hole 112. When heat is transferred from one side of the core layer 110 to the other, the amount of heat conducted through the metallic layer 126 is quite limited because the cross-sectional area of the metallic layer 126 perpendicular to the thermal path is relatively small. In other words, the metallic layer 126 inside the hole 112 can not provide optimal heat dissipation effect and electrical performance.